Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine and a laser printer employing an electro-photographic technique.
Description of the Related Art
In an image forming apparatus configured to transfer a toner image formed on a belt such as an intermediate transfer belt onto a recording material, if the intensity of a transfer field is too strong when the toner image is transferred onto the recording medium, an electric discharge may occur and cause a so-called “white spot phenomenon” in which a white void region is formed on an image.
The electric discharge that causes the white spot phenomenon occurs in a space between the belt and the recording material, and the white spot phenomenon is likely to occur if the belt vibrates in the vicinity of a transfer portion.
Therefore, Japanese Patent Application Laid-Open No. 2002-82543 discusses a configuration in which a vibration prevention sheet is pressed against an inner circumferential surface of the belt in order to suppress vibration of the belt in the vicinity of the transfer portion.
However, as illustrated in (a) of FIG. 2, if the length of the vibration prevention sheet in a width direction of the belt is set to be shorter than the width of the belt, end portions of the vibration prevention sheet contact the rear surface of the belt. Because tensile force is applied to the belt through a tension roller, as illustrated in (b) of FIG. 2, stress from the vibration prevention sheet applied to the belt is concentrated in the vicinity of the end portions of the vibration prevention sheet, so that a large quantity of particles scraped from the belt will be generated.
Further, in a case where the belt is provided with a correction mechanism for correcting the movement (deviation) of the belt in the width direction thereof, the stress is further concentrated at end portions X in the moving direction of the belt as illustrated in FIG. 3, so that the scraping of the belt will be accelerated.
If the generated scraped particles adhere to the rollers that constitute the transfer portion, they may gradually enter the image region while the belt is being moved continuously, and variation in the transfer electric field may arise, which in turn may cause image defects.